The traditional solid-state foaming process is a well-characterized method of producing microcellular thermoplastic foams. This process has been applied to a variety of crystalline and amorphous polymers, including polystyrene (PS), polycarbonate (PC), and polyethylene terephthalate (PET). Cell nucleation is achieved by a rapid reduction in the gas solubility of the polymer by the introduction of heat and/or rapid depressurization.
Further developments in the solid-state process have sought to produce polymer foams with cells in the sub-micron range. Reducing the cell size of polymer foams is a significant goal due to predicted improvements in the strength-to-weight ratio, toughness, and thermal insulation. Some methods of reducing the cell size have included the use of nanocomposite additives as nucleation sites, the foaming of polymer blends with nanoscale domains, and the use of specialized block copolymers with CO2-philic blocks.
This disclosure relates to a method for producing foams having nanoscale features that are suitable to be used as battery separators in cells.